SAN YSIDRO  The $741 million reconfiguration of the San Ysidro port of entry hinges entirely on federal funding. Now a newly unveiled proposal for a complementary private project near the busiest crossing on the U.S.-Mexico border envisions parking spots, retail space — even a rooftop heliport for ambulance crews and Customs and Border Protection officers.

With an estimated cost of $30 million to $50 million, the proposed mixed-use structure would help replace 1,500 parking places that are being lost with the latest phase of the San Ysidro port’s reconstruction — the rebuilding of the southernmost stretch of Interstate 5.

“It’s taken all these years to think of something that we think the community will be proud of and what the border needs,” Simon Falic, chairman and chief operating officer of Duty Free Americas, the proposal’s proponent, said Monday.

Duty Free Americas owns the UETA Duty-Free Store in San Ysidro and its adjacent 1,500-space parking lot. The company expects both the lot and store to disappear with the realignment of I-5, which will connect the freeway directly to Mexico’s El Chaparral border crossing.

Falic said his business has begun negotiations with the U.S. General Services Administration, the agency overseeing the port reconstruction. The company, which expects to lose 12 acres through eminent domain, hopes to build the mixed-use structure on a three-acre parcel on the same site or in an adjacent location owned by the federal government.

The structure would include 900 parking spots and house a UETA store. It would also include space for drivers waiting to pick up pedestrian crossers from Mexico—free of charge for a limited time.

“We are now meeting with (Customs and Border Protection) at some of the highest levels to ensure that what is put forth is understood and that it meets all requirements,” said former CBP commissioner David Aguilar, one of the project’s consultants.

The proposal has won the endorsement of San Ysidro’s business community. “This is parking for my stores, my businesses,” said Jason Wells, executive director of the San Ysidro Chamber of Commerce and spokesman for the San Ysidro Smart Border Coalition. “It’s solving a problem for my community that is not being answered by the federal government.”

To design the project, Duty Free Americas has engaged the services of HNTB Corp., a Kansas City-based firm that collaborated in the $907 million expansion of Terminal 2 at San Diego International Airport.

A General Services Administration spokeswoman said in a statement Monday that the agency “is preparing to enter into good-faith negotiations with a local property owner to acquire real property for ... the realignment of the final segment of the southbound I-5 freeway.” But the statement did not name the property owner, explaining that “due to the sensitive nature of these negotiations, we are unable to discuss specific details at this point.”

The federal reconfiguration project, scheduled for completion in 2018, is moving forward thanks to $226 million in funding approved by Congress this year. The phase involving I-5 is meant to increase efficiency for southbound drivers. Since El Chaparral’s opening in October 2012, southbound traffic has been funneled down to a narrow and temporary roadway built by the Mexican government.